/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8                               :vi │
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
│                                                                              │
│ Permission to use, copy, modify, and/or distribute this software for         │
│ any purpose with or without fee is hereby granted, provided that the         │
│ above copyright notice and this permission notice appear in all copies.      │
│                                                                              │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
│ PERFORMANCE OF THIS SOFTWARE.                                                │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/runtime/runtime.h"
#include "libc/str/str.h"
#include "libc/sysv/errfuns.h"

/**
 * Removes environment variable.
 *
 * @param name is non-empty environment key which can't contain `'='`
 * @return 0 on success, or -1 w/ errno and environment is unchanged
 * @raise EINVAL if `name` is an empty string or has a `'='` character
 * @threadunsafe
 */
int unsetenv(const char *name) {

  if (!name || !*name || strchr(name, '='))
    return einval();

  long k = 0;
  for (long i = 0; environ[i]; ++i) {
    bool matches = false;
    for (long j = 0;; ++j) {
      if (!name[j]) {
        matches = !environ[i][j] || environ[i][j] == '=';
        break;
      }
      if (name[j] != environ[i][j])
        break;
    }
    if (!matches)
      environ[k++] = environ[i];
  }
  environ[k] = 0;

  return 0;
}
